An image sensor is a semiconductor device for converting an optical image into an electrical signal. An image sensor may be classified as a charge coupled device (CCD) image sensor or a complementary metal oxide semiconductor (CMOS) image sensor (CIS).
The CIS may include a plurality of photodiodes and MOS transistors within a unit pixel for sequentially detecting electrical signals of respective unit pixels in a switching manner to realize an image.
The CIS may further include forming a microlens on and/or over a color filter to enhance light sensitivity of the CIS. The microlens may be formed in a semicircular/hemispherical shape by sequentially performing an exposure process, a development process, and a reflow process on a photosensitive organic material.
However, since the photosensitive organic material has weak physical properties and thus, the microlens may be easily damaged by physical impacts that may result in cracking, etc. in subsequent processes such as packaging and bumping, etc. Since the photosensitive organic material has relatively strong viscosity, a defect on the microlens may develop when particles are absorbed. In order to prevent this occurrence, use of a passivation layer composed of an oxide layer or a nitride layer having high hardness may be used or composing the microlens of inorganic material. Moreover, since the upper portion of the CIS is formed of a photosensitive organic material vulnerable to heat of 250° C. or more, an interface trap by a plasma process may occur. Accordingly, such damaging effects to the microlens may result in the generation of a dark current.